Evidence of the survival of ectopically transplanted oral mucosal epithelial stem cells after repeated wounding of cornea

Cell therapy in the cornea: The emerging role of microenvironment

The cornea is an ideal testing field for cell therapies. Its highly ordered structure, where specific cell populations are sequestered in different layers, together with its accessibility, has allowed the development of the first stem cell-based therapy approved by the European Medicine Agency. Today, different techniques have been proposed for autologous and allogeneic limbal and non-limbal cell transplantation. Cell replacement has also been attempted in cases of endothelial cell decompensation as it occurs in Fuchs dystrophy: injection of cultivated allogeneic endothelial cells is now in advanced phases of clinical development. Recently, stromal substitutes have been developed with excellent integration capability and transparency. Finally, cell-derived products, such as exosomes obtained from different sources, have been investigated for the treatment of severe corneal diseases with encouraging results. Optimization of the success rate of cell therapies obviously requires high-quality cultured cells/products, but the role of the surrounding microenvironment is equally important to allow engraftment of transplanted cells, to preserve their functions and, ultimately, lead to restoration of tissue integrity and transparency of the cornea.

Lack of Elevated Expression of TGFβ3 Contributes to the Delay of Epithelial Wound Healing in Diabetic Corneas

Purpose

To investigate the mechanisms underlying the differential roles of TGFβ1 and TGFβ3 in accelerating corneal epithelial wound healing (CEWH) in diabetic (DM) corneas, with normoglycemia (NL) corneas as the control.

Methods

Two types of diabetic mice, human corneal organ cultures, mouse corneal epithelial progenitor cell lines, and bone marrow-derived macrophages (BMDMs) were employed to assess the effects of TGFβ1 and TGFβ3 on CEWH, utilizing quantitative PCR, western blotting, ELISA, and whole-mount confocal microscopy.

Results

Epithelial debridement led to an increased expression of TGFβ1 and TGFβ3 in cultured human NL corneas, but only TGFβ1 in DM corneas. TGFβ1 and TGFβ3 inhibition was significantly impeded, but exogenous TGFβ1 and, more potently, TGFβ3 promoted CEWH in cultured TKE2 cells and in NL and DM C57BL6 mouse corneas. Wounding induced similar levels of p-SMAD2/SMAD3 in NL and DM corneas but weaker ERK1/2, Akt, and EGFR phosphorylation in DM corneas compared to NL corneas. Whereas TGFβ1 augmented SMAD2/SMAD3 phosphorylation, TGFβ3 preferentially activated ERK, PI3K, and EGFR in healing DM corneas. Furthermore, TGFβ1 and TGFβ3 differentially regulated the expression of S100a9, PAI-1, uPA/tPA, and CCL3 in healing NL and DM corneas. Finally, TGFβ1 induced the expression of M1 macrophage markers iNOS, CD86, and CTGF, whereas TGFβ3 promoted the expression of M2 markers CD206 and NGF in BMDMs from db/db or db/+ mice.

Conclusions

Hyperglycemia disrupts the balanced expression of TGFβ3/TGFβ1, resulting in delayed CEWH, including impaired sensory nerve regeneration in the cornea. Supplementing TGFβ3 in DM wounds may hold therapeutic potential for accelerating delayed wound healing in diabetic patients.

Animal Models for Limbal Stem Cell Deficiency: A Critical Narrative Literature Review

This literature review will provide a critical narrative overview of the highlights and potential pitfalls of the reported animal models for limbal stem cell deficiency (LSCD) and will identify the neglected aspects of this research area. There exists significant heterogeneity in the literature regarding the methodology used to create the model and the predefined duration after the insult when the model is supposedly fully fit for evaluations and/or for testing various therapeutic interventions. The literature is also replete with examples wherein the implementation of a specific model varies significantly across different studies. For example, the concentration of the chemical, as well as its duration and technique of exposure in a chemically induced LSCD model, has a great impact not only on the validity of the model but also on the severity of the complications. Furthermore, while some models induce a full-blown clinical picture of total LSCD, some are hindered by their ability to yield only partial LSCD. Another aspect to consider is the nature of the damage induced by a specific method. As thermal methods cause more stromal scarring, they may be better suited for assessing the anti-fibrotic properties of a particular treatment. On the other hand, since chemical burns cause more neovascularisation, they provide the opportunity to tap into the potential treatments for anti-neovascularisation. The animal species (i.e., rats, mice, rabbits, etc.) is also a crucial factor in the validity of the model and its potential for clinical translation, with each animal having its unique set of advantages and disadvantages. This review will also elaborate on other overlooked aspects, such as the anaesthetic(s) used during experiments, the gender of the animals, care after LSCD induction, and model validation. The review will conclude by providing future perspectives and suggestions for further developments in this rather important area of research.

New developments in the management of persistent corneal epithelial defects

A persistent epithelial defect (PED) is a corneal epithelial defect that failed to heal after 2weeks. It is a condition that carries much morbidity, and our understanding of PED remains poor, with current treatment methods often having unsatisfactory outcomes. With PEDs becoming more prevalent, more efforts are required to establish reliable treatment modalities. Our reviews describe the causes of PEDs and the different approaches developed to manage them, as well as their associated limitations. Emphasis is placed on understanding various advances in the development of new treatment modalities. We have also described a case of a woman with a background of graft-versus-host disease on long-term topical corticosteroids who developed complicated PED involving both eyes. The current approach to managing PEDs generally involves exclusion of an active infection, followed by treatment modalities that aim to encourage corneal epithelial healing. Success rates, however, remain far from desirable, as treatment remains challenging due to multiple underlying etiologies. In summary, advances in the development of new therapies may be able to facilitate progress in the understanding and treatment of PED.

Comparison between Cultivated Oral Mucosa and Ocular Surface Epithelia for COMET Patients Follow-Up

Total bilateral Limbal Stem Cell Deficiency is a pathologic condition of the ocular surface due to the loss of corneal stem cells. Cultivated oral mucosa epithelial transplantation (COMET) is the only autologous successful treatment for this pathology in clinical application, although abnormal peripheric corneal vascularization often occurs. Properly characterizing the regenerated ocular surface is needed for a reliable follow-up. So far, the univocal identification of transplanted oral mucosa has been challenging. Previously proposed markers were shown to be co-expressed by different ocular surface epithelia in a homeostatic or perturbated environment. In this study, we compared the transcriptome profile of human oral mucosa, limbal and conjunctival cultured holoclones, identifying Paired Like Homeodomain 2 (PITX2) as a new marker that univocally distinguishes the transplanted oral tissue from the other epithelia. We validated PITX2 at RNA and protein levels to investigate 10-year follow-up corneal samples derived from a COMET-treated aniridic patient. Moreover, we found novel angiogenesis-related factors that were differentially expressed in the three epithelia and instrumental in explaining the neovascularization in COMET-treated patients. These results will support the follow-up analysis of patients transplanted with oral mucosa and provide new tools to understand the regeneration mechanism of transplanted corneas.

Advancements in Ocular Regenerative Therapies

The use of stem cells (SCs) has emerged as a promising avenue in ophthalmology, offering potential therapeutic solutions for various vision impairments and degenerative eye diseases. SCs possess the unique ability to self-renew and differentiate into specialised cell types, making them valuable tools for repairing damaged tissues and restoring visual function. Stem cell-based therapies hold significant potential for addressing conditions such as age-related macular degeneration (AMD), retinitis pigmentosa (RP), corneal disorders, and optic nerve damage. Therefore, researchers have explored different sources of stem cells, including embryonic stem cells (ESC), induced pluripotent stem cells (iPSCs), and adult stem cells, for ocular tissue regeneration. Preclinical studies and early-phase clinical trials have demonstrated promising outcomes, with some patients experiencing improved vision following stem cell-based interventions. However, several challenges remain, including optimising the differentiation protocols, ensuring transplanted cells' safety and long-term viability, and developing effective delivery methods. The field of stem cell research in ophthalmology witnesses a constant influx of new reports and discoveries. To effectively navigate these tons of information, it becomes crucial to summarise and systematise these findings periodically. In light of recent discoveries, this paper demonstrates the potential applications of stem cells in ophthalmology, focusing on their use in various eye tissues, including the cornea, retina, conjunctiva, iris, trabecular meshwork, lens, ciliary body, sclera, and orbital fat.

SOX2 Is a Univocal Marker for Human Oral Mucosa Epithelium Useful in Post-COMET Patient Characterization

Total bilateral Limbal Stem Cells Deficiency is a pathologic condition of the ocular surface due to loss or impairment of corneal stem cell function, altering homeostasis of the corneal epithelium. Cultivated Oral Mucosa Epithelial Transplantation (COMET) is the only autologous treatment for this pathology. During the follow-up, a proper characterization of the transplanted oral mucosa on the ocular surface supports understanding the regenerative process. The previously proposed markers for oral mucosa identification (e.g., keratins 3 and 13) are co-expressed by corneal and conjunctival epithelia. Here, we propose a new specific marker to distinguish human oral mucosa from the epithelia of the ocular surface. We compared the transcriptome of holoclones (stem cells) from the human oral mucosa, limbal and conjunctival cultures by microarray assay. High expression of SOX2 identified the oral mucosa vs. cornea and conjunctiva, while PAX6 was highly expressed in corneal and conjunctival epithelia. The transcripts were validated by qPCR, and immunological methods identified the related proteins. Finally, the proposed markers were used to analyze a 10-year follow-up aniridic patient treated by COMET. These findings will support the follow-up analysis of COMET treated patients and help to shed light on the mechanism of corneal repair and regeneration.

Direct oral mucosal epithelial transplantation supplies stem cells and promotes corneal wound healing to treat refractory persistent corneal epithelial defects

Persistent corneal epithelial defects (PED) can lead to irreversible blindness, seriously affecting the social function and life quality of these patients. When it comes to refractory PED, such as limbal stem cell deficiency (LSCD), that does not respond to standard managements, stem cell therapy is an ideal method. Oral mucosal epithelium (OME) abundant with stem cells within the base, is a promising autologous biomaterial, with much resemblance to corneal epithelial structures. In this experiment, uncultured autologous rat OME was directly applied to alkali burned corneas. Clinical evaluations and histological analyses showed that the transplantation accelerated the healing process, presenting faster re-epithelization and better formation of corneal epithelial barrier. To further investigate the therapeutic mechanism, oral epithelium was transplanted to de-epithelialized cornea in vitro for organ culture. It could be observed that the oral epithelial cells could migrate to the corneal surface and form smooth and stratified epithelium. Immunofluorescence staining results showed that the re-formed epithelium derived from OME, maintained stemness and transformed to corneal epithelial phenotype to some extent. Corneal stroma may provide the suitable microenvironment to promote the trans-differentiation of oral stem cells. Thus, both in vivo and in vitro experiments suggested that oral epithelium could play a positive role in treating refractory PED.

Goals and Challenges of Stem Cell-Based Therapy for Corneal Blindness Due to Limbal Deficiency

Corneal failure is a highly prevalent cause of blindness. One special cause of corneal failure occurs due to malfunction or destruction of the limbal stem cell niche, upon which the superficial cornea depends for homeostatic maintenance and wound healing. Failure of the limbal niche is referred to as limbal stem cell deficiency. As the corneal epithelial stem cell niche is easily accessible, limbal stem cell-based therapy and regenerative medicine applied to the ocular surface are among the most highly advanced forms of this novel approach to disease therapy. However, the challenges are still great, including the development of cell-based products and understanding how they work in the patient's eye. Advances are being made at the molecular, cellular, and tissue levels to alter disease processes and to reduce or eliminate blindness. Efforts must be coordinated from the most basic research to the most clinically oriented projects so that cell-based therapies can become an integrated part of the therapeutic armamentarium to fight corneal blindness. We undoubtedly are progressing along the right path because cell-based therapy for eye diseases is one of the most successful examples of global regenerative medicine.

Measurement of the Adipose Stem Cells Cell Sheets Transmittance

In the field of cell therapy, the interest in cell sheet technology is increasing. To determine the cell sheet harvesting time requires experience and practice, and different factors could change the harvesting time (variability among donors and culture media, between cell culture dishes, initial cell seeding density). We have developed a device that can measure the transmittance of the multilayer cell sheets, using a light emitting diode and a light detector, to estimate the harvesting time. The transmittance of the adipose stromal cells cell sheets (ASCCS) was measured every other day as soon as the cells were confluent, up to 12 days. The ASCCS, from three different initial seeding densities, were harvested at 8, 10, and 12 days after seeding. Real-time PCR and immunostaining confirmed the expression of specific cell markers (CD29, CD73, CD90, CD105, HLA-A, HLA-DR), but less than the isolated adipose stromal cells. The number of cells per cell sheets, the average thickness per cell sheet, and the corresponding transmittance showed no correlation. Decrease of the transmittance seems to be correlated with the cell sheet maturation. For the first time, we are reporting the success development of a device to estimate ASCCS harvesting time based on their transmittance.

Regenerative Medicine of Epithelia: Lessons From the Past and Future Goals

This article explores examples of successful and unsuccessful regenerative medicine on human epithelia. To evaluate the applications of the first regenerated tissues, the analysis of the past successes and failures addresses some pending issues and lay the groundwork for developing new therapies. Research should still be encouraged to fill the gap between pathologies, clinical applications and what regenerative medicine can attain with current knowledge.

Subconjunctival Injection of Transdifferentiated Oral Mucosal Epithelial Cells for Limbal Stem Cell Deficiency in Rats

Rat limbal niche cells (LNCs) have been proven to induce transdifferentiation of oral mucosal epithelial cells (OMECs) into corneal epithelial-like cells termed transdifferentiated oral mucosal epithelial cells (T-OMECs). This investigation aimed to evaluate the effect of subconjunctival T-OMEC injections on alkali-induced limbal stem cell deficiency (LSCD) in rats. LNCs were cocultured with OMECs in the Transwell system to obtain T-OMECs, with NIH-3T3 cells serving as a control. Subconjunctival injection of single T-OMEC or OMEC suspension was performed immediately after corneal alkali injury. T-OMECs were prelabeled with the fluorescent dye CM-DiI in vitro and tracked in vivo. Corneal epithelial defect, opacity, and neovascularization were quantitatively analyzed. The degree of corneal epithelial defect (from day 1 onward), opacity (from day 5 onward), and neovascularization (from day 2 onward) was significantly less in the T-OMEC group than in the OMEC group. Cytokeratin 12 (CK12), pigment epithelium-derived factor, and soluble fms-like tyrosine kinase-1 were expressed at a higher rate following T-OMEC injection. Some CM-DiI-labeled cells were found to be coexpressed with CK12, Pax6, and ΔNp63α in the corneal epithelium after subconjunctival injection. Subconjunctival injection of T-OMECs prevents conjunctival invasion and maintains a normal corneal phenotype, which might be a novel strategy in the treatment of LSCD.

Bioengineering Approaches for Corneal Regenerative Medicine

BACKGROUND

Since the cornea is responsible for transmitting and focusing light into the eye, injury or pathology affecting any layer of the cornea can cause a detrimental effect on visual acuity. Aging is also a reason for corneal degeneration. Depending on the level of the injury, conservative therapies and donor tissue transplantation are the most common treatments for corneal diseases. Not only is there a lack of donor tissue and risk of infection/rejection, but the inherent ability of corneal cells and layers to regenerate has led to research in regenerative approaches and treatments.

METHODS

In this review, we first discussed the anatomy of the cornea and the required properties for reconstructing layers of the cornea. Regenerative approaches are divided into two main categories; using direct cell/growth factor delivery or using scaffold-based cell delivery. It is expected delivered cells migrate and integrate into the host tissue and restore its structure and function to restore vision. Growth factor delivery also has shown promising results for corneal surface regeneration. Scaffold-based approaches are categorized based on the type of scaffold, since it has a significant impact on the efficiency of regeneration, into the hydrogel and non-hydrogel based scaffolds. Various types of cells, biomaterials, and techniques are well covered.

RESULTS

The most important characteristics to be considered for biomaterials in corneal regeneration are suitable mechanical properties, biocompatibility, biodegradability, and transparency. Moreover, a curved shape structure and spatial arrangement of the fibrils have been shown to mimic the corneal extracellular matrix for cells and enhance cell differentiation.

CONCLUSION

Tissue engineering and regenerative medicine approaches showed to have promising outcomes for corneal regeneration. However, besides proper mechanical and optical properties, other factors such as appropriate sterilization method, storage, shelf life and etc. should be taken into account in order to develop an engineered cornea for clinical trials.

Vitrification and storage of oral mucosa epithelial cell sheets

Shipping time and shipping delays might affect the quality of the stem cells based engineered "organs." In our laboratory, we have developed a limbal stem cell deficient (LSCD) rabbit model. To reverse the LSCD, we cultured oral mucosal epithelial cells for 2-3 weeks and engineered cultured autologous oral mucosa epithelial cell sheets (CAOMECS), which were grafted on the LSCD cornea. The purpose of this study was to vitrify CAOMECS and to store it until the CAOMECS can be grafted onto patients. CAOMECS were vitrified in LN₂ for up to 204 days. We tested two different methods of vitrification with different solutions; however, CAOMECS were only viable when they were not stored in a vitrification solution; results were only reported from this CAOMECS. On the basis of hematoxylin and eosin staining, we showed that the CAOMECS morphology was well preserved after long-term storage in LN₂ . Most of the preservation solutions maintained the CAOMECS phenotype (Ki67, proliferating cell nuclear antigen (PCNA), Beta-Catenin, ZO-1, E-Cadherin, CK3, CK4, CK13). The exception was the solution composed with ethylene glycol and Dimethyl sulfoxide (DMSO): this resulted in loss of DeltaN-p63 expression. DeltaN-p63 is an important marker for cell proliferation. The expression of proteins involved in cell-cell connection and the differentiation markers were maintained. Apoptosis was not detected in the thawed CAOMECS. We demonstrated that CAOMECS can be stored long-term in LN₂ without affecting their morphology and phenotype.

Transplantation of oral mucosal epithelial cells seeded on decellularized and lyophilized amniotic membrane for the regeneration of injured endometrium

Background

Intrauterine adhesion (IUA) is characterized by progressive intrauterine fibrosis as a consequence of trauma to the basal layer of the endometrium. In an attempt to relieve IUA, many approaches have been applied in the clinic but show limited effects. In this study, we investigated the effect of autologous oral mucosal epithelial cells (OMECs) seeded on decellularized and lyophilized amniotic membrane (DL-AM) on preventing the development of IUA in a rat model.

Methods

IUA model was established by surgical scraping of the endometrium in the left uteri (the right uteri were kept as control) of SD rats. Wounds were randomly treated as unrepaired (IUA group), repaired with DL-AM alone (DL-AM group), and DL-AM seeded with autologous OMECs (DL-AM+OMECs group), respectively, in a total of 54 rats (n = 18 each). Uterus samples were harvested for histological and immunohistochemical evaluation after 3, 7, 14, and 28 days (n = 3 in each time point) of operations.

Results

After surgery, the uterine cavity was observed to be filled with extensive fibrosis in the IUA and DL-AM groups, respectively, while a lower ratio of the fibrotic area was identified in the DL-AM transplantation group. Transplantation of OMECs seeded on DL-AM significantly reduced fibrosis of IUA with recovered uterine cavity and regenerated epithelium and endometrial glands as determined by CK-18 immunostaining. OMECs transplantation resulted in extensive cellular proliferation as revealed by the Ki-67 immunofluorescent staining exhibited. Meanwhile, microvessel density was significantly increased in uteri that received OMECs transplantation, which was concomitant with elevated expression of vascular endothelial growth factor. The pregnancy test (n = 6 in each group) showed successful conception in the OMEC-transplanted uteri, but not in the IUA and DL-AM groups.

Conclusions

Engineered epithelium developed from DL-AM seeded with OMECs showed great potential in preventing progression of intrauterine adhesion by improved endometrial epithelium regeneration.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1179-z) contains supplementary material, which is available to authorized users.

Explant culture of oral mucosal epithelial cells for fabricating transplantable epithelial cell sheet

Introduction

Carrier-free autologous mucosal epithelial cell sheets have been clinically utilized as a cell therapy for various epithelial disorders. Fabrication of a transplantable oral mucosal epithelial cell sheet without mouse feeder layers requires a higher seeding density than that of a sheet with mouse feeder layer culture; therefore, a large amount of donor mucosal tissue is needed. However, cell grafts co-cultured with mouse feeder layers are classified by the US Food and Drug Administration (FDA) as xenogeneic products. The goal of this study was to evaluate the utility of oral mucosal epithelial cells expanded by primary explant culture for the fabrication of an adequate number of transplantable epithelial cell sheets without mouse feeder layers.

Methods

Small fragments derived from minced oral mucosal tissue were placed into culture dishes for primary explant culture in keratinocyte culture medium. After primary explant culture, the outgrown cells were treated with trypsin-EDTA and were seeded on a temperature-responsive cell culture insert. After subculture, the cultured cells were harvested as a confluent cell sheet from the culture vessel by temperature reduction.

Results

Carrier-free human oral mucosal epithelial cell sheets were fabricated in all human cases, and autologous transplantation of the harvested cell sheets showed rapid epithelial regeneration to cover epithelial defects in a rabbit model. The explant culture method, involving the use of small fragments for primary culture, was sufficient for preparing a large number of mucosal epithelial cells without mouse feeder layers. Moreover, oral mucosal epithelial cells derived from the primary explant culture after cryopreservation allowed for the fabrication of cell sheets.

Conclusions

This method for fabricating transplantable oral mucosal epithelial cell sheets is an attractive technique for regenerative medicine. It offers a patient-friendly manufacturing method in which a small amount of biopsy material from the patient represents a sufficient epithelial cell source, and a manufacturing plan for preparing cell grafts can be easily tailored.

Preventive effects of transplantation of oral mucosal epithelial cells seeded on a decellularized amniotic membrane in a model of intrauterine adhesion

OBJECTIVE

To observe the preventive effects of oral mucosal epithelial cells (OMECs) seeded on a decellularized human amniotic membrane (dHAM) in a rat model of intrauterine adhesion (IUA).

METHODS

IUAs were established by mechanical endometrial scraping in model rats. Thirty-six Sprague-Dawley rats were divided into: IUA, dHAM transplantation, and dHAM+OMECs transplantation groups (12 in each group). The oral mucosae of rats were collected, and the OMECs were cultured on the dHAM. The dHAM and dHAM+OMECs were transplanted into left scraped uteri (right uteri as controls) in the dHAM and dHAM+OMECs transplantation groups. At 3, 7, 14, and 28 days after transplantation, the uterine samples underwent histological and immunohistochemical staining.

RESULTS

After endometrial scraping, the endometria and uterine cavities were obliterated. The ratios of the fibrotic areas to the whole endometrium in the IUA and dHAM transplantation group were higher than in the control group (P<0.01). In the dHAM+OMECs transplantation group, the fibrotic area significantly decreased compared to the IUA group after 7, 14, and 28 days, and the dHAM transplantation group at 14 and 28 days (P<0.01). At 14 and 28 days after surgery in the dHAM+OMECs transplantation group, the number of endometrial glands and the endometrial thickness increased (P<0.01), and regenerated epithelia were observed. Immunohistochemical assays for cytokeratin 18 demonstrated that the newly-regenerated epithelium was endometrium.

CONCLUSION

OMECs can enhance repair of damaged endometrium, and promise to be novel and effective in preventing IUAs. However, studies of OMECs in patients with IUA need further exploration.

The promise of stem cell-based therapeutics in ophthalmology

The promising role of cellular therapies in the preservation and restoration of visual function has prompted intensive efforts to characterize embryonic, adult, and induced pluripotent stem cells for regenerative purposes. Three main approaches to the use of stem cells have been described: sustained drug delivery, immunomodulation, and differentiation into various ocular structures. Studies of the differentiation capacity of all three types of stem cells into epithelial, neural, glial and vascular phenotypes have reached proof-of-concept in culture, but the correction of vision is still in the early developmental stages, and the requirements for effective in vivo implementation are still unclear. We present an overview of some of the preclinical findings on stem-cell rescue and regeneration of the cornea and retina in acute injury and degenerative disorders.

Storage Temperature Alters the Expression of Differentiation-Related Genes in Cultured Oral Keratinocytes

Purpose

Storage of cultured human oral keratinocytes (HOK) allows for transportation of cultured transplants to eye clinics worldwide. In a previous study, one-week storage of cultured HOK was found to be superior with regard to viability and morphology at 12°C compared to 4°C and 37°C. To understand more of how storage temperature affects cell phenotype, gene expression of HOK before and after storage at 4°C, 12°C, and 37°C was assessed.

Materials and Methods

Cultured HOK were stored in HEPES- and sodium bicarbonate-buffered Minimum Essential Medium at 4°C, 12°C, and 37°C for one week. Total RNA was isolated and the gene expression profile was determined using DNA microarrays and analyzed with Partek Genomics Suite software and Ingenuity Pathway Analysis. Differentially expressed genes (fold change > 1.5 and P < 0.05) were identified by one-way ANOVA. Key genes were validated using qPCR.

Results

Gene expression of cultures stored at 4°C and 12°C clustered close to the unstored control cultures. Cultures stored at 37°C displayed substantial change in gene expression compared to the other groups. In comparison with 12°C, 2,981 genes were differentially expressed at 37°C. In contrast, only 67 genes were differentially expressed between the unstored control and the cells stored at 12°C. The 12°C and 37°C culture groups differed most significantly with regard to the expression of differentiation markers. The Hedgehog signaling pathway was significantly downregulated at 37°C compared to 12°C.

Conclusion

HOK cultures stored at 37°C showed considerably larger changes in gene expression compared to unstored cells than cultured HOK stored at 4°C and 12°C. The changes observed at 37°C consisted of differentiation of the cells towards a squamous epithelium-specific phenotype. Storing cultured ocular surface transplants at 37°C is therefore not recommended. This is particularly interesting as 37°C is the standard incubation temperature used for cell culture.

Concise review: transplantation of cultured oral mucosal epithelial cells for treating limbal stem cell deficiency-current status and future perspectives

A number of diseases and external factors can deplete limbal stem cells, causing pain and visual loss. Ten years have passed since the first transplantation of cultured oral mucosal epithelial cells in humans, representing the first autologous cell-based therapy for severe bilateral limbal stem cell deficiency. Its steady increase in popularity since then can be attributed to the accumulating evidence of its efficacy in reverting limbal stem cell deficiency. In this review, the focus is on clinical, and to a lesser degree laboratory, features of cultured oral mucosal epithelial transplants over the past 10 years. Comparisons with other available technologies are made. Avenues for research to stimulate further improvements in clinical results and allow worldwide distribution of limbal stem cell therapy based on oral mucosal cells are discussed. These include storage and transportation of cultured oral mucosal epithelial sheets and in vivo culture of oral mucosal epithelial cells.

Culture of Oral Mucosal Epithelial Cells for the Purpose of Treating Limbal Stem Cell Deficiency

The cornea is critical for normal vision as it allows allowing light transmission to the retina. The corneal epithelium is renewed by limbal epithelial cells (LEC), which are located in the periphery of the cornea, the limbus. Damage or disease involving LEC may lead to various clinical presentations of limbal stem cell deficiency (LSCD). Both severe pain and blindness may result. Transplantation of cultured autologous oral mucosal epithelial cell sheet (CAOMECS) represents the first use of a cultured non-limbal autologous cell type to treat this disease. Among non-limbal cell types, CAOMECS and conjunctival epithelial cells are the only laboratory cultured cell sources that have been explored in humans. Thus far, the expression of p63 is the only predictor of clinical outcome following transplantation to correct LSCD. The optimal culture method and substrate for CAOMECS is not established. The present review focuses on cell culture methods, with particular emphasis on substrates. Most culture protocols for CAOMECS used amniotic membrane as a substrate and included the xenogeneic components fetal bovine serum and murine 3T3 fibroblasts. However, it has been demonstrated that tissue-engineered epithelial cell sheet grafts can be successfully fabricated using temperature-responsive culture surfaces and autologous serum. In the studies using different substrates for culture of CAOMECS, the quantitative expression of p63 was generally poorly reported; thus, more research is warranted with quantification of phenotypic data. Further research is required to develop a culture system for CAOMECS that mimics the natural environment of oral/limbal/corneal epithelial cells without the need for undefined foreign materials such as serum and feeder cells.

Non-Triple Helical Form of Type IV Collagen α1 Chain

Type IV collagen with a triple-helical structure composed of three α chains is a major component of basement membrane. Previously, we reported that non-triple helical form of type IV collagen α1 chain (NTHα1(IV)) was isolated from human placenta and the culture media of human cells. In the present study, we report on the localization of NTH α1(IV) with a monoclonal antibody #370, exclusively reactive for the nascent chain, in the rabbit tissues. The staining was found on the basement membrane of blood vessels, of endomysium, of nerve, and of kidney but not on epithelial basement membrane. In a rabbit angiogenic model, #370 antibody staining was exclusively observed in neovascular tip region of endothelial cells, where no staining with anti-type IV collagen antibody was seen. Distinct localizations suggest that NTHα1(IV) is produced and stably deposited in endothelial cells and the surroundings under physiological conditions with some physiological roles in relation to the dynamics of vascular system.

Characterization of rabbit limbal epithelial side population cells using RNA sequencing and single-cell qRT-PCR

Corneal epithelial stem cells reside in the limbus, a transitional zone between the cornea and conjunctiva, and are essential for maintaining homeostasis in the corneal epithelium. Although our previous studies demonstrated that rabbit limbal epithelial side population (SP) cells exhibit stem cell-like phenotypes with Hoechst 33342 staining, the different characteristics and/or populations of these cells remain unclear. Therefore, in this study, we determined the gene expression profiles of limbal epithelial SP cells by RNA sequencing using not only present public databases but also contigs that were created by de novo transcriptome assembly as references for mapping. Our transcriptome data indicated that limbal epithelial SP cells exhibited a stem cell-like phenotype compared with non-SP cells. Importantly, gene ontology analysis following RNA sequencing demonstrated that limbal epithelial SP cells exhibited significantly enhanced expression of mesenchymal/endothelial cell markers rather than epithelial cell markers. Furthermore, single-cell quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) demonstrated that the limbal epithelial SP population consisted of at least two immature cell populations with endothelial- or mesenchymal-like phenotypes. Therefore, our present results may propose the presence of a novel population of corneal epithelial stem cells distinct from conventional epithelial stem cells.

Remodeling of epithelial cells and basement membranes in a corneal deficiency model with long-term follow-up

The ocular surface consists of the cornea, conjunctiva, and the limbus that is located in the transitional zone between the cornea and conjunctiva. The corneal epithelial cells are generated through the mitosis of corneal epithelial stem cells in the limbus. This study investigated a rabbit corneal deficiency model prepared by the surgical removal of the corneal and limbal epithelia, which express cytokeratin 12 (K12). After the surgery, K13-expressing conjunctival epithelium migrated onto the corneal surface and completely covered the surface, leading to neovascularization and corneal opacification. However, at 24 and 48 weeks after the surgery, K12-expressing cornea-like cells reappeared on the model ocular surface. These cells formed an island surrounded by invaded conjunctiva and were isolated from the limbus. Interestingly, in the 24-week model surface, α1(IV) and α2(IV) collagen chains, which are normally found in the basement membrane of the native limbus and conjunctiva, and not in the cornea, were continuously deposited throughout the entire basement membrane, including the basement membrane under cornea-like cells. By contrast, in the 48-week model surface, α1(IV) and α2(IV) collagen chains were absent from the basement membrane beneath the central part of cornea-like cells and were localized below the invaded conjunctiva and the transitional zone between cornea-like cells and the invaded conjunctiva, which had similar distribution to the native ocular basement membrane. Moreover, K12, K14, p63, vimentin, and α1(IV) and α2(IV) collagen chains, which are colocalized in the native limbus, were all present at the transitional zone of the 48-week model surface. Therefore, a limbus-like structure appeared to be reconstructed on the surface of the 48-week model as a stem cell niche. This study should aid in the understanding of human corneal deficiency, the correlation between the epithelial cell phenotype and the composition of the basement membrane, and the epithelial stem cell niche.